The over all objective to be pursued will be to gain a more complete understanding of the structure relationships of the periodontal ligament (PDL) fibroblasts and their totipotential role in maintaining the periodontal apparatus. Emphasis will be directed to further characterization of the PDL fibroblast cell surface using the freeze-fracture technique. Special emphasis will be devoted to determining the nature, and distribution of cell-to-matrix and cell-to-cell contacts. The relationship of the subsurface cytoplasmic filaments to membrane particles and cell-to-matrix contacts will be investigated by using deep etching techniques. The particle distribution of cytoplasmic membranes will be established as a means of characterizing various cytoplasmic domains in relation to the secretory process. Having previously carried out detailed electron microscopic autoradiographic (EM-ARG) studies of collagen secretion by PDL fibroblasts in vivo, it is appropriate that similar EM-ARG studies of the synthesis of non-collagenous matrix proteins be carried out. Con A and cationic ferritin binding to PDL fibroblasts will be studied and correlated to freeze-fracture IMP distributions and the EM-ARG results of glycoprotein secretion. Moreover, the activity of PDL fibroblasts adjacent to sites of bone resorption will be examined for collagen phagocytosis, synthesis and secretion and ability to differentiate into new osteoblasts. Finally, the ultrastructural features and synthetic capacity of PDL fibroblasts will be studied in early, established and advanced lesions of periodontal disease and compared to normal PDL fibroblasts.